Surface coated rigid polyurethane foam with durable flame retardancy and improved mechanical property

High loading of flame retardants are usually required to prepare fire safety rigid polyurethane foam (RPUF), which often leads to deterioration of its mechanical properties. In this work, a silicone resin (poly-DDPM) was synthesized and coated on the surface of RPUF in association with expandable graphite (EG) via brush painting in order to improve its flame retardancy with minimal damage to the inherent mechanical property. The flammability characterization by limiting oxygen index (LOI), UL 94 and cone calorimeter tests revealed that the fire resistance of the foam samples was significantly improved by the presence of poly-DDPM/EG coating with an average add on of 8.5 mg/cm2. The LOI value was increased to 32.3 from 18, the UL 94 grade was upgraded to V-0, the peak heat release rate and the peak smoke release rate was reduced 55% and 59% respectively compared with that of the control RPUF sample. Additionally, the coated sample could not be ignited when it was exposed to a butane burner for 10 min. The compressive strength of the coated RPUF was impressively increased 10%. Furthermore, the fire resistance of the coating was durable under artificial harsh weather conditions. The poly-DDPM/EG coating adhered on the RPUF surface tightly, and transformed into expanded graphite flakes loaded nano-silica to achieve a protective char layer upon combustion. The demonstrated coated RPUF has great potential for commercial products.